1. Technical Field
This invention relates to a counter assembly for use in conjunction with a fluid meter to provide flow volume information corrected to a standard. In particular, the invention is concerned with an improvement in a portion of the drive mechanism for a mechanical computer arrangement contained within the counter assembly to provide for the correction of a measure of actual flow.
2. Background Information
Typically, meters used to measure the flow of gases, such as natural gas, measure in quantities of cubic feet. With natural gas being sold on a cubic foot basis it is important both from the supplier's standpoint and the consumer's standpoint that the heating value of each cubic foot purchased be constant. However, the heating value of a cubic foot of natural gas changes dependent upon both temperature and pressure. As a result, measured quantities of gas are corrected to standard cubic feet. A standard cubic foot is representative of an amount of gas which occupies a cubic foot of space at a standard temperature and pressure. Under normal service conditions, changes in the temperature of the gas are more dramatic and likely to have a much greater effect upon the correction to standard than are the changes in the pressure of the gas.
To provide for corrections due to temperature, gas meters include counters with mechanical computers which correct measured volumes of gas flow to standard. Generally, the way in which this is done is to convert the constant directional rotational motion of the meter rotors into oscillating arcuate motion and then to change the length of the arc based upon the difference in temperature from standard. A more detailed description of one form of counter employing the foregoing principle is described in U.S. Pat. No. 3,581,566. Another arrangement utilizing this same principle is disclosed in U.S. Pat. No. 3,969,939. As disclosed in this latter patent, the rotational motion of the output of the constant displacement rotors of the meter is converted by means of a crank wheel and lever link into an oscillating arcuate motion of a radial arm. An outer end of the arm, thus swings along an arcuate path. Positioned within the path is a cam surface whose location controls the length of the arc through which the end of the arm swings. The location of the can surface within the path changes dependent upon temperature, either lengthening or shortening the arcuate swing of the arm. The arm itself is attached to the input hub of a one-way clutch so that, when the end of the arm swings from a start position most distant from the cam surface toward the cam surface no relative motion is transmitted through the hub to an output shaft connected to a register. However, when the arm swings away from the cam surface, back toward its start position, rotational motion is transferred to the output shaft. The amount of rotation of the output shaft represents a gas flow volume through the meter corrected for temperature.
In driving the input hub, a lost motion spring connection is provided between the crank wheel and the input hub so that when the computer arm engages the temperature cam the crank can continue to rotate without parts in the drive connection to the input hub binding. One arrangement for this purpose is shown in U.S. Pat. No. 3,969,939 wherein a slot is provided in the link allowing the crank pin to slide within the link when further movement of the link at its connection to the computer arm is halted by the outer end of the arm engaging the cam surface.